Investigate BlobDB as storage for da blobs

[bacv]

At the moment attested chunks/blobs are supposed to be written and read from the files (da_blob_dir/app_id_hex/vid_hex).

Depending on the sizes of the blob it's worth investigating BlobDB where blobs could be stored as values and metadata app_id+index as keys.

Assuming the api is very similar to the RocksDB, BlobDB could be implemented as another storage service backend and swapped to in da related services.